Quantum dot LED and OLED integration for high efficiency displays

ABSTRACT

Displays including hybrid pixels including an OLED subpixel and QD-LED subpixel are described. In an embodiment, OLED and QD-LED stacks are integrated into the same pixel with multiple common layers shared by the OLED and QD-LED stacks.

RELATED APPLICATIONS

This application claims the priority of U.S. Provisional Application No.62/290,423 filed on Feb. 2, 2016, which is incorporated herein byreference.

BACKGROUND Field

Embodiments described herein relate to display systems. Moreparticularly, embodiments relate to display systems with hybrid emissivelight emitting diodes (LEDs).

Background Information

State of the art displays for phones, tablets, computers and televisionsutilize glass substrates with thin-film transistors (TFT) to controltransmission of backlight through pixels based on liquid crystals. Morerecently emissive displays such as those based on organic light emittingdiodes (OLED) have been introduced because they can have a fasterresponse time, and be more power efficient, allowing each pixel to beturned off completely when displaying black or dark colors, and becompatible with plastic substrates. Even more recently, quantum dotlight emitting diodes (QD-LEDs) have been introduced as an alternativedisplay technology, potentially being more power efficient that OLEDs.

SUMMARY

Display systems and hybrid pixel arrangements are described. In anembodiment, a display includes a hybrid pixel with an OLED subpixel anda QD-LED subpixel. A common hole transport layer is in the OLED subpixeland the QD-LED subpixel. A quantum dot layer is over the common holetransport layer in the QD-LED subpixel, and an organic emission layerthat includes a phosphorescent material is over the common holetransport layer in the OLED subpixel. A common electron transport layeris over the quantum dot layer in the QD-LED subpixel, and over theorganic emission layer in the OLED subpixel. A common top electrodelayer is over the common electron transport layer in the OLED subpixeland the QD-LED subpixel.

In an embodiment, a method of forming a display includes forming acommon hole transport layer over a display backplane in using a firstsolution technique, where the common hole transport layer is formed overthe display backplane in an OLED subpixel and a QD-LED subpixel. Aquantum dot layer is then formed over the common hole transport layer inthe QD-LED subpixel. An organic emission layer including aphosphorescent material may then be evaporated over the common holetransport layer in the OLED subpixel. A common electron transport layermay be evaporated over the quantum dot layer in the QD-LED subpixel, andover the organic emission layer in the OLED subpixel, A common topelectrode layer may then be formed over the common electron transportlayer in the OLED subpixel and the QD-LED subpixel.

In an embodiment, a display includes a tandem hybrid pixel including anOLED subpixel and a QD-LED subpixel. A common hole transport layer is inthe OLED subpixel and the QD-LED subpixel. A common quantum dot layer isover the common hole transport layer in the QD-LED subpixel and in theOLED subpixel. A semi-common charge generation layer is over the commonquantum dot layer in the OLED subpixel. A first cathode is over thecommon quantum dot layer in the QD-LED subpixel. A semi-common holetransport layer is over the semi-common charge generation layer in theOLED subpixel. An organic emission layer is over the semi-common holetransport layer in the OLED subpixel. A semi-common electron transportlayer is over the organic emission layer in the OLED subpixel, and asemi-common second cathode is over the semi-common electron transportlayer in the OLED subpixel. In an embodiment, a common nanoparticleelectron transport layer including metal-oxide nanoparticles is over thecommon quantum dot layer in the QD-LED subpixel and in the OLEDsubpixel, the semi-common charge generation layer is over the commonnanoparticle electron transport layer in the OLED subpixel, and thefirst cathode is over the common nanoparticle electron transport layerin the QD-LED subpixel.

In an embodiment, a display includes a tandem hybrid pixel including anOLED subpixel and a QD-LED subpixel. A common hole transport layer is inthe OLED subpixel and the QD-LED subpixel. A common quantum dot layer isover the common hole transport layer in the QD-LED subpixel and in theOLED subpixel. A common charge generation layer is over the commonquantum dot layer in the OLED subpixel and in the QD-LED subpixel, and acommon hole transport layer is over the common charge generation layerin the OLED subpixel and in the QD-LED subpixel. An organic emissionlayer is over the common hole transport layer in the OLED subpixel. Acommon electron transport layer is over the common hole transport layerin the OLED subpixel and in the QD-LED subpixel, and the common electrontransport layer is additionally over the organic emission layer in theOLED subpixel. A common cathode is over the common electron transportlayer in the OLED subpixel and in the QD-LED subpixel. In an embodiment,a common nanoparticle electron transport layer including metal-oxidenanoparticles is over the common quantum dot layer in the QD-LEDsubpixel and in the OLED subpixel, and the common charge generationlayer is over the common nanoparticle electron transport layer in theOLED subpixel and in the QD-LED subpixel.

In an embodiment a display with a tandem QD-LED and OLED tandem stackincludes a common anode, a common hole transport layer over the commonanode, a common quantum dot layer over the common hole transport layer,a common charge generation layer over the common quantum dot layer. acommon hole transport layer over the common charge generation layer, acommon organic emission layer over the common hole transport layer, acommon electron transport layer over the common organic emission layer,and a common cathode over the common electron transport layer. In anembodiment, the tandem QD-LED and OLED tandem stack further includes asecond common organic emission layer between the common organic emissionlayer and the common electron transport layer. In an embodiment, thetandem QD-LED and OLED tandem stack further includes a second commonelectron transport layer over the common organic emission layer, asecond charge generation layer over the second common electron transportlayer, and a second hole transport layer over the second chargegeneration layer, where the second common organic emission layer is overthe second hole transport layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an energy diagram of the layers in a QD-LED stack inaccordance with an embodiment.

FIG. 2 is an energy diagram of the layers in a QD-LED stack including ametal oxide nanoparticle electron transport layer in accordance with anembodiment.

FIG. 3 is an energy diagram of the layers in a QD-LED stack including aninsulating layer between a quantum dot layer and a metal oxidenanoparticle electron transport layer in accordance with an embodiment.

FIG. 4 is an energy diagram of the layers in a QD-LED stack including ahole transport layer with modified energy levels in accordance with anembodiment.

FIG. 5 is an energy diagram of the layers in a QD-LED stack including ametal oxide nanoparticle hole transport layer in accordance with anembodiment.

FIG. 6 is a schematic cross-sectional side view illustration of a hybridpixel including a patterned quantum dot layer in accordance with anembodiment.

FIGS. 7-10 are schematic cross-sectional side view illustrations ofhybrid pixels including a common quantum dot layer in accordance withembodiments.

FIG. 11 is a schematic cross-sectional side view illustration of aninverted hybrid pixel including a common quantum dot layer in accordancewith an embodiment.

FIGS. 12-18 are schematic cross-sectional side view illustrations ofhybrid pixels including tandem structure stacks in accordance withembodiments.

FIGS. 19-20 are schematic cross-sectional side view illustrationsblended emission tandem structure stacks in accordance with embodiments.

DETAILED DESCRIPTION

Embodiments describe display systems with hybrid pixels. In anembodiment, a display includes a hybrid pixel including an OLED subpixeland a QD-LED subpixel. A common hole transport layer is in the OLEDsubpixel and the QD-LED subpixel with commonly shared layers. A quantumdot (QD) layer is over the common hole transport layer in the QD-LEDsubpixel. In some embodiments, the QD layer is a common layer over thecommon hole transport layer in the OLED subpixel and the QD-LEDsubpixel. An organic emission layer is over the common hole transportlayer in the OLED subpixel. In some embodiments the organic emissionlayer is over the common QD layer in the OLED subpixel. A commonelectron transport layer is over the QD layer in the QD-LED subpixel andover the organic emission layer in the OLED subpixel. A common topelectrode layer is over the common electron transport layer in the OLEDsubpixel and the QD-LED subpixel.

While power efficiency for OLEDs is a potential benefit of OLEDdisplays, conventional fluorescent OLEDs are known to have a maximuminternal quantum efficiency (IQE) of around 25%. Phosphorescent OLEDsystems may be more efficient, and can have IQE values approaching 100%.As such, it may be advantageous to employ phosphorescent OLED materialsin displays. Red and green phosphorescent OLED devices have highefficiencies, saturated colors, and acceptable lifetimes. For bluephosphorescent materials, however, available materials tend to haveunacceptably short lifetime, unsaturated colors, or both. As such, thereis a need to improve the blue emitter system in an OLED display, whilemaintaining the acceptable performance of red and green phosphorescentmaterials.

In an embodiment, a hybrid pixel includes a blue-emitting QD-LED pixeland one or more emitting OLED subpixels, such as a green-emitting OLEDsubpixel and a red-emitting OLED subpixel in a RGB hybrid pixel layout.In a specific embodiment, the red OLED subpixel and green OLED subpixelinclude phosphorescent OLED materials. It is to be appreciated that anRGB hybrid pixel layout is exemplary, and embodiments are not solimited. Other exemplary pixel arrangements includered-green-blue-yellow-cyan (RBGYC), red-green-blue-white (RGBW), orother sub-pixel matrix schemes where the pixels have a different numberof sub-pixels.

In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions andprocesses, etc., in order to provide a thorough understanding of theembodiments. In other instances, well-known display processes andmanufacturing techniques have not been described in particular detail inorder to not unnecessarily obscure the embodiments. Reference throughoutthis specification to “one embodiment” means that a particular feature,structure, configuration, or characteristic described in connection withthe embodiment is included in at least one embodiment. Thus, theappearances of the phrase “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment. Furthermore, the particular features, structures,configurations, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms “above”, “over”, “to”, “between”, and “on” as used herein mayrefer to a relative position of one layer with respect to other layers.One layer “above”, “over”, or “on” another layer may be directly incontact with the other layer or may have one or more intervening layers.One layer “between” layers may be directly in contact with the layers ormay have one or more intervening layers.

Referring now to FIGS. 1-5 various cross-sectional side viewillustrations are provided of QD-LED stacks in accordance withembodiments. In the particular embodiments illustrated (including thoseillustrated in FIGS. 6-9), a dashed outline is provided around a groupof layers that may be fabricated using solution-based processing. Thesegroupings are exemplary, and intended to visually illustrate thepotential impact of solution-based processing, however, the embodimentsare not limited to solution-based processing. In one aspect, increasingthe ratio of solution-based processed layers can potentially lead toincreased performance and reduced cost of fabrication. For example,solution-based processing may have a reduced time of production comparedto evaporation techniques. Solution-based processing of layers maypotentially reduce the number of processing steps, and increase yield.For example, solution-based process may negate concerns with exposingevaporated species to air, solvent, etc. In some embodiments,solution-based processing is implemented only prior to the formation ofan organic layer by thermal evaporation.

FIG. 1 is an energy diagram of the layers in a QD-LED stack inaccordance with an embodiment. As shown, the QD-LED stack may include ananode 110, a hole injection layer (HIL) 120 on/over the anode 110, ahole transport layer (HTL) 130 on/over the HIL 120, a QD layer 140on/over the HTL 130, an electron transport layer (ETL) 150 on/over theQD layer 140, an electron injection layer (EIL) 160 on/over the ETL 150,and a cathode 170 on/over the EIL 160. As described and illustratedherein a layer on/over another layer may be directly on (in contact)with the other layer or may have or more intervening layers. Inoperation, a voltage is applied across the QD-LED stack such that theanode is positive with respect to the cathode. Current flows through theQD-LED stack from the cathode to anode, as electrons are injected fromthe cathode 170 into the lowest unoccupied molecular orbital (LUMO) ofthe QD layer 140, while electrons are withdrawn toward the anode 110from the highest occupied molecular orbital (HOMO) of the QD layer 140(alternately described as hole injection into the HOMO of the QD layer140). Recombination of electrons and holes in the QD layer 140 isaccompanied by emission of radiation, the frequency of which dependentupon the band gap of the QDs, or the difference in energy (eV) betweenthe HOMO and LUMO. It is to be appreciated that the particular energylevels illustrated in FIGS. 1-5 are exemplary, and that the energylevels are variable. Accordingly, the particular energy levelsillustrated are provided for illustrative purposes only, and embodimentsare not limited to the specific energy levels illustrated.

Still referring to FIG. 1, an anode 110 is formed on a displaysubstrate, such as a TFT substrate, or substrate includingredistribution lines. Anode 110 may be formed of a variety ofelectrically conductive materials. In an embodiment, anode 110 is formedof indium-tin-oxide (ITO). For example, ITO may be formed by sputteringor thermal evaporation. In an embodiment, an array of anodes 110 issputtered onto a display substrate through a mask, such as a fine metalmask, with a separate anode 110 formed in each subpixel.

As shown, a HIL 120 is formed on the anode 110. In accordance withembodiments, the HIL 120 may be a common layer shared by multiplesubpixels within a pixel, and may be a common layer across multiplepixels. The HIL 120 facilitates the injection of positive charge (holes)from the anode 110 into the HTL 130. The HIL 120 may be formed ofmaterials such as conductive polymer-based materials (e.g. polythiophenes, poly anilines), combination of arylamine based holetransport host and electron accepting dopant (e.g. charge transfersalts), strongly electron accepting small organic molecules, metaloxides. The HIL 120 may be formed using techniques such as spin coating,ink jet printing, slot die coating, nozzle printing, contact printing,gravure printing, any solution printing technology, as well as thermalevaporation.

As shown, a HTL 130 is formed on the HIL 120. In accordance withembodiments, the HTL 130 may be a common layer shared by multiplesubpixels within a pixel, and may be a common layer across multiplepixels. The HTL 130 transports positive charge (holes) to the QD layer140, the emissive layer in the QD-LED stack, and physically separatesthe HIL 120 from the QD layer 140. HTL 130 may be formed of electronrich materials such as arylamines, polyfluorene derivatives, andnanoparticle metal oxides (e.g. NiO). The HTL 130 may be formed usingtechniques such as spin coating, ink jet printing, slot die coating,nozzle printing, contact printing, gravure printing, any solutionprinting technology, as well as thermal evaporation.

As shown, a QD layer 140 is formed on the HTL 130. In accordance withembodiments, the QD layer 140 may be formed or patterned only in aQD-LED subpixel, or the QD layer 140 may be a common layer shared bymultiple subpixels within a pixel, or may be a common layer acrossmultiple pixels. The QD layer 140 may be formed of light emittingsemiconductor nanoparticles that emit light at desired wavelength andfull width at half max. Exemplary nanoparticles include spherical, rodshaped, platelet (2D quantum well) including semiconductor materialssuch as CdSe, InP, GaSe, etc. The QD layer 140 may be formed usingtechniques such as spin coating, ink jet printing, slot die coating,nozzle printing, contact printing, gravure printing, and any solutionprinting technology. In an embodiment QD layer 140 may be formed bytransfer printing an array of QD layers 140 into an array of subpixels.

As shown, an ETL 150 is formed on the QD layer 140. In accordance withembodiments, the ETL 150 may be a common layer shared by multiplesubpixels within a pixel, and may be a common layer across multiplepixels. The ETL 150 may be a high electron mobility layer thattransports negative charge (electrons) into the QD layer 140 andphysically separates the EIL 160 from the QD layer 140. ETL 150 may beformed of electron deficient materials such as organometallic compounds,organic small molecules (e.g. substituted benzimidazoles), andnanoparticle metal oxides (e.g. ZnO). The ETL 150 may be formed usingtechniques such as spin coating, ink jet printing, slot die coating,nozzle printing, contact printing, gravure printing, any solutionprinting technology, as well as thermal evaporation.

As shown, an EIL 160 is formed on the ETL 150. In accordance withembodiments, the EIL 160 may be a common layer shared by multiplesubpixels within a pixel, and may be a common layer across multiplepixels. The EIL 160 facilitates the injection of negative charge(electrons) from the electrode into the ETL 150. EIL 160 may be formedof alkali metal salts such as LiF, low work function metals such as Ca,Ba, and n-doped material (e.g. combination of electron transportmaterial and electron donating material). In an embodiment, the EIL 160is formed by thermal evaporation.

As shown, a cathode 170 is formed on the EIL 160. Cathode 170 may beformed of a variety of electrically conductive materials, includingtransparent or semi-transparent materials. In accordance withembodiments, the cathode 170 may be a common layer shared by multiplesubpixels within a pixel, and may be a common layer across multiplepixels. In an embodiment, cathode 170 is formed of materials such asCa/Mg, Sm/Au, Yb/Ag, Ca/Ag, Ba/Ag, and Sr/Ag. For example, in a doublelayer Ca/Mg the Ca layer has a low work-function for electron injection,whereas a Mg capping layer improves electrical conductance of thecathode 170. In an embodiment, cathode 170 is formed by thermalevaporation.

Referring now to FIG. 2, an energy diagram similar to FIG. 1 is providedwith the addition of a nanoparticle ETL 180 formed between the QD layer140 and the ETL 150 in accordance with an embodiment. In an embodiment,nanoparticle ETL 180 includes an assembly of metal oxide nanoparticles,such as ZnO nanoparticles. In the embodiment illustrated, nanoparticleETL 180 facilitates the transport of electrons from ETL 150 to the QDlayer 140 and physically separates the QDs within QD layer 140 from anorganic ETL 150. In an embodiment, ETL 180 is formed using a techniquesuch as spin coating, ink jet printing, slot die coating, nozzleprinting, contact printing, gravure printing, and any solution printingtechnology. In an embodiment ETL 180 may be formed by transfer printingan array of ETLs 180 into an array of subpixels. In an embodiment,transfer printing includes transferring an ETL 180/QD layer 140 stack.

Referring now to FIG. 3, an energy diagram similar to FIG. 2 is providedwith the addition of an insulating layer 185 formed between the QD layer140 and the nanoparticle ETL 180 in accordance with an embodiment. Theinsulating layer 185 may function to modulate electron current into theQD layer 140, or more specifically electron injection from thenanoparticle ETL 180 to the QD layer 140 in order to mitigate excesselectron current. This modulation may be adjusted by composition andthickness of the insulating layer 185. In an embodiment, the insulatinglayer is nanometers to tens of nanometers thick. In an embodiment,insulating layer 185 is formed of poly (methyl methacrylate) (PMMA). Inan embodiment, insulating layer 185 is formed using a technique such asspin coating, ink jet printing, slot die coating, nozzle printing,contact printing, gravure printing, and any solution printingtechnology. In an embodiment insulating layer 185 may be formed bytransfer printing an array of insulating layers 185 into an array ofsubpixels. In an embodiment, transfer printing includes transferring anETL 180/insulating layer 185/QD layer 140 stack.

Referring now to FIG. 4, an energy diagram similar to FIG. 2 is providedwith modified energy levels of the HTL 130 in accordance with anembodiment. For example, the HOMO and LUMO energy levels of the HTL 130may be modified by the use of non-traditional deep HOMO based compoundsto more closely match the QD HOMO energy level. In an embodiment, theenergy difference between the HTL 130 HOMO energy level and the QD layer140 HOMO energy level is less than 0.5 eV with the inclusion ofnon-traditional deep HOMO based compounds for HTL 130. Exemplarymaterials include nanoparticle metal oxides (e.g. NiO), and organicbased molecules (e.g. acene and carbazole derivative based compounds,carbizole derivative based polymers, polyphenylenes, derivatizedtriphenylenes). In an embodiment, HTL 130 is formed using any techniquepreviously described for HTL 130.

Referring now to FIG. 5, an energy diagram similar to FIG. 4 is providedwith the addition of a metal oxide nanoparticle HTL 190 between the QDlayer 140 and the HTL 130 in accordance with an embodiment. In anembodiment, metal oxide nanoparticle HTL 190 includes an assembly ofmetal oxide nanoparticles, such as NiO nanoparticles. In the embodimentillustrated, nanoparticle HTL 190 facilitates the transport of holesfrom HTL 130 to the QD layer 140 and physically separates the QDs withinQD layer 140 from an organic HTL 130. The HTL 190 may be formed usingtechniques such as spin coating, ink jet printing, slot die coating,nozzle printing, contact printing, gravure printing, and any solutionprinting technology. In an embodiment HTL 190 may be formed by transferprinting an array of HTLs 190 into an array of subpixels. In anembodiment, transfer printing includes transferring an HTL 190/QD layer140 stack. In an embodiment, transfer printing includes transferring anHTL 190/QD layer 140/ETL 180 stack. In an embodiment, transfer printingincludes transferring an HTL 190/QD layer 140//insulating layer 185/ETL180 stack.

Referring now to FIGS. 6-9 various hybrid pixel layouts are provided toillustrate the integration of QD-LED and OLED subpixels within adisplay. In particular, the illustrated hybrid pixel layouts are basedupon the QD-LED stack structures illustrated and described with regardto FIGS. 1, 2 and 4. However, these illustrations are exemplary and mayinclude additional layers, such as insulating layer 185 and HTL 190.Accordingly, the implementation of insulating layer 185 and HTL 190 isnot limited to the embodiments illustrated and described with regard toFIGS. 3 and 5.

In the case of electroluminescent displays, the red, green, and bluesubpixels within a single display pixel are comprised of an assembly oflayers common to all three subpixels and layers specific to a particularsubpixel. In accordance with some embodiments, the common layers in thehybrid pixel may include the HIL 120, HTL 130, and ETL 150, EIL 150, andcathode 170 layer. In some embodiments, the layers specific to eachsubpixel may include the buffer transport layers (BTLs) 210 and theemissive layers (e.g. organic emission layers 200-R, 200-G, and QD layer140). In some embodiment, the BTL 210 and/or QD layer 140 may be commonlayers. The thickness of the common layers and BTLs 210 are selected toensure specific micro cavity design for each of the red, green, and bluesubpixels. In the hybrid pixel assembly, the BTLs 210 have two roles—oneis to further adjust the cavity strength as well as to ensure that thelayer next to the emissive layer has a band gap higher than that of theemissive species itself. In the case of the red and green phosphorescentorganic emission layers 200-R, 200-G, the BTL 210 should have a tripletenergy that is higher than the triplet energy of the emitter material.Furthermore, the BTL 210 energy levels (HOMO, LUMO) may be selected tofacilitate hole or electron blocking functionality next to the emissivelayer.

FIG. 6 is a schematic cross-sectional side view illustration of a hybridpixel including a patterned QD layer 140 in accordance with anembodiment. In the embodiment illustrated, separate anodes 110-R, 110-G,110-B are provided for each separate subpixel (e.g. RBG). A common HIL120 and common HTL 130 are formed over the separate anodes 110-R, 110-G,110-B.

In the particular embodiment illustrated in FIG. 6, the blue-emittingQD-LED subpixel includes a QD layer 140 formed on the common HTL 130,and a nanoparticle ETL 180 (e.g. ZnO nanoparticles) formed on the QDlayer 140. In one embodiment, the QD layer 140 and nanoparticle ETL 180are formed using any of the previously described solution-basedtechniques. In another embodiment, the QD layer 140 and nanoparticle ETL180 are transfer printed either separately, or together as a layerstack. Following the formation of the QD layer 140 and nanoparticle ETL180, the remainder of the layers may be fabricated, for example, bythermal evaporation.

Still referring to FIG. 6, buffer transport layers 210-R, 210-G areformed on the common HTL 130, followed by the formation of red and greenemitting organic emission layers 200-R, 200-G on the BTLs 210-R, 210-G.In the arrangement illustrated in FIG. 6, 210-R, 210-G are BTLs in thered and green OLED subpixels, and are both serving as electron blockinglayers. Exemplary materials may include carbazole and triphenylene basedorganic compounds, which may be formed by thermal evaporation. A commonETL 150 may then be formed on the organic emission layers 200-R, 200-G,and the nanoparticle ETL 180. A common EIL 160 may then be formed overthe common ETL 150, followed by the formation of a common cathode 170layer.

As shown in FIG. 6, the hybrid pixel arrangement includes a QD-LED stackstructure similar to that illustrated in FIG. 2 or FIG. 4. In otherembodiments, the hybrid pixel arrangement may optionally include aninsulating layer 185, and/or HTL 190 as previously described with regardto FIGS. 3 and 5. Additionally, the nanoparticle ETL 180 may optionallybe removed.

Referring now to FIGS. 7-9 additional hybrid pixel arrangements areillustrated including a common QD layer 140 in accordance withembodiments. In such arrangements, additional processing operationsassociated with patterning the QD layer 140 may be removed, which mayreduce time of production. This may additionally eliminate resolution(e.g. pixels per inch) constraints related to patterning or printing.

FIG. 7 is a schematic cross-sectional side view illustration of a hybridpixel similar to FIG. 6, with common QD layer 140, and no nanoparticleETL 180. Additionally, the optional BTLs 210-R, 210-G are removed. Inthe embodiment illustrated, the common ETL 150 is formed on organicemission layers 200-R, 200-G in the OLED subpixels, and on the common QDlayer 140 in the QD-LED subpixel.

FIG. 8 is a schematic cross-sectional side view illustration of a hybridpixel similar to FIG. 6, with common QD layer 140, and commonnanoparticle ETL 180 formed on the common QD layer 140. In theembodiment illustrated, the common ETL 150 is formed on organic emissionlayers 200-R, 200-G in the OLED subpixels, and on the commonnanoparticle ETL 180 in the QD-LED subpixel.

FIG. 9 is a schematic cross-sectional side view illustration of a hybridpixel similar to FIG. 7, with BTLs 210-R, 210-G formed on the organicemission layers 200-R, 200-G, respectively. The BTLs 210-R, 210-G inFIG. 9 are distinguishable from the BTLs illustrated in FIGS. 6 and 8,in that the BTLs 210-R, 210-G in FIG. 9 serve as hole blocking layers asopposed to electron blocking layers. Exemplary materials for BTLsserving as hole blocking layers may include organometallic wide band gapcompounds (hole blocking) and other organic compounds (e.g. substitutedbenzimidazoles), which may be formed by thermal evaporation.

FIG. 10 is a schematic cross-sectional side view illustration of ahybrid pixel similar to FIG. 9, with a common BTL 210 being formed onthe organic emission layers 200-R, 200-G and common QD layer 140, asopposed to separate BTLs being formed in each OLED subpixel

In other embodiments, the hybrid pixel arrangements illustrated in FIGS.7-9 may optionally include a common insulating layer 185, and/or commonHTL 190 as previously described with regard to FIGS. 3 and 5.

FIG. 11 is a schematic cross-sectional side view illustration of aninverted hybrid pixel including a common QD layer 140 in accordance withan embodiment. In the embodiment illustrated, separate cathodes 170-R,170-G, 170-B are provided for each separate subpixel (e.g. RBG). In anembodiment, the cathodes 170-R, 170-G, 170-B are formed of ITO. A commonnanoparticle ETL 180 is formed over the separate cathodes 170-R, 170-G,170-B, followed by the formation of a common QD layer 140 over thecommon nanoparticle ETL 180. Similar to the arrangements illustrated inFIGS. 7-10, the arrangement in FIG. 11 may eliminate the resolutionconstraints associated with patterning or printing. Still referring toFIG. 11, organic emission layers 200-R, 200-G are formed on the QD layer140, followed by the formation of BTLs 210-R, 210-G on the organicemission layers 200-R, 200-G, respectively, for example using thermalevaporation. A common HTL 130 is then formed on the BTLs 210-R, 210-G inthe OLED subpixels, and the common QD layer 140 in the QD-LED subpixel.A common HIL 192 may then be formed over the common HTL 130, forexample, using thermal evaporation. Exemplary materials of HIL 192include hexaazatriphenylene-hexacarbonitrile (HAT-CN) or molybdenumoxide (MoOx). A common anode 110 layer is then formed over the commonHIL 192. In an embodiment, the common anode 110 layer is formed ofaluminum.

Referring now to FIGS. 12-18 various configurations of hybrid pixelsincluding tandem structure stacks are provided in accordance withembodiments, in which multiple emitting units are stacked vertically.Referring to FIG. 12, a QD layer 140, HTL 130, HIL 120 may be formedover separate anodes 110-R, 110-G, 110-B similarly as previouslydescribed with regard to FIG. 7, followed by the formation of a commonETL 150 over the common QD layer 140 in the OLED subpixels and theQD-LED subpixel. A separate cathode 170-B may then be formed on thecommon ETL 150 in the QD-LED subpixel, while a semi-common chargegeneration layer (CGL) 220 is formed on the common ETL 150 in the OLEDsubpixels. As illustrated, the semi-common CBL 220 is common to the OLEDsubpixels only.

In accordance with embodiments, the CGL 220 is used to connect anassembly of two emissive layers in tandem with each other. It providespositive (hole) current to the upper (with reference to the figures)emissive layers (e.g. 200-R, 200-G) and negative (electron) current tothe lower emissive layer (e.g. QD layer 140). Typically a CGL 220 iscomprised of two distinct layers. For example, the electron current canbe provided by a layer comprised of alkali metal salts such as LiF, lowwork function metals such as Ca, Ba, and n-doped material (e.g.combination of electron transport material and electron donatingmaterial). The hole current can be provided by a layer comprised ofcombination of arylamine based hole transport host and electronaccepting dopant (e.g. charge transfer salts), strongly electronaccepting small organic molecules, metal oxides. In accordance withembodiments, CGL 220 is formed by thermal evaporation.

A semi-common HIL 120 may then be formed on the semi-common CGL 220,followed by the formation of a semi-common HTL 130 on the semi-commonHIL 120. Organic emission layers 200-R, 200-G may then be formed on thesemi-common HTL 130 in separated OLED subpixels. A semi-common ETL 150may then be formed over both organic emission layers 200-R, 200-G,followed by the formation of a semi-common EIL 160, and a semi-commoncathode 170 in both OLED subpixels. A red color filter 230-R mayoptionally be formed over the semi-common cathode 170 in the redemitting OLED subpixel, and a green color filter 230-G may optionally beformed over the semi-common cathode 170 in the green emitting OLEDsubpixel.

FIG. 13 is a schematic cross-sectional side view illustration of ahybrid pixel including a tandem structure stack similar to that providedin FIG. 12 with one difference being the substitution of nanoparticleETL 180 in place of ETL 150. Additionally, nanoparticle ETL 180 may befabricated using a solution-based technique.

FIG. 14 is a schematic cross-sectional side view illustration of ahybrid pixel including a tandem structure stack similar to that providedin FIG. 13 with one difference being the addition of semi-common ETL 150between the semi-common CGL 220 and the semi-common HIL 120.

Referring now to FIG. 15 a schematic cross-sectional side viewillustration of a hybrid pixel including a tandem structure stack isprovided in accordance with an embodiment in which the QD-LED subpixelis inverted. As shown, a common nanoparticle ETL 180 may be formed overseparate anodes 110-R, 110-G, and cathode 170-B. In an embodiment,anodes 110-R, 110G, and cathode 170-B are formed of the same material,such as ITO. A common QD layer 140 may then be formed over the commonnanoparticle ETL 180. The common nanoparticle ETL 180 and common QDlayer 140 may be formed using solution-based techniques. A common HTL130 may then be formed over the common QD layer 140, followed by theformation of a common HIL 192 over the common HTL 130, for example bythermal evaporation. An anode 110-B may then be formed on the common HIL192 in the QD-LED subpixel, while a semi-common HTL 130 is formed on thecommon HIL 192 in the OLED subpixels.

BTLs 210-R, 210-G are then formed on the semi-common HTL 130 in thered-emitting and green-emitting OLED subpixels, followed by theformation of organic emission layers 200-R, 200-G on the BTLs 210-R,210-G. In the arrangement illustrated in FIG. 15, 210-R, 210-G are BTLsin the red and green OLED subpixels, and are both serving as electronblocking layers. Exemplary materials may include carbazole andtriphenylene based organic compounds, which may be formed by thermalevaporation. A semi-common ETL 150 is then formed over the organicemission layers 200-R, 200-G, followed by the formation of a semi-commonEIL 160 on the semi-common ETL 150, and a semi-common cathode 170 on thesemi-common EIL 160.

Referring now to FIGS. 16-18, schematic cross-sectional side viewillustrations of hybrid pixels including tandem structure stacks areprovided similar to those in FIGS. 12-14 with one difference being thata separate cathode 170 is not provided for the QD-LED subpixel, and thepreviously described and illustrated semi-common layers are now commonlayers across both the OLED subpixels and the QD-LED subpixel.Additionally, a blue color filter 230-B may be formed over the commoncathode 170 layer in the QD-LED subpixel.

FIGS. 19-20 are schematic cross-sectional side view illustrationsblended emission tandem structure stacks in accordance with embodiments.As such, the structures illustrated in FIGS. 19-20 may be utilized toemit a blended spectrum, such as white light. As illustrated in FIGS.19-20, each layer may be a common layer formed on top of another commonlayer. In both embodiments illustrated in FIGS. 19-20, the ETL 150formed above the solution-based layers may be substituted with asolution-based nanoparticle ETL 180, or ETL 150 may be formed on top ofa solution-based nanoparticle ETL 180.

In utilizing the various aspects of the embodiments, it would becomeapparent to one skilled in the art that combinations or variations ofthe above embodiments are possible for forming hybrid OLED/QD-LEDpixels. Although the embodiments have been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the appended claims are not necessarily limited to thespecific features or acts described. The specific features and actsdisclosed are instead to be understood as embodiments of the claimsuseful for illustration.

What is claimed is:
 1. A display comprising: a hybrid pixel including anorganic light emitting diode (OLED) subpixel and a quantum dot lightemitting diode (QD-LED) subpixel; a common hole transport layer in theOLED subpixel and the QD-LED subpixel; a common quantum dot layer overthe common hole transport layer in the QD-LED subpixel and the QD-LEDsubpixel; an organic emission layer over the common hole transport layerin the OLED subpixel and over the common quantum dot layer in the OLEDsubpixel, wherein the organic emission layer comprises a phosphorescentmaterial; a common electron transport layer over the common quantum dotlayer in the QD-LED subpixel, and over the organic emission layer in theOLED subpixel; a common top electrode layer over the common electrontransport layer in the OLED subpixel and the QD-LED subpixel.
 2. Thedisplay of claim 1, further comprising: a common hole injection layer inthe OLED subpixel and the QD-LED subpixel; wherein the common holetransport layer is over the common hole injection layer in the OLEDsubpixel and the QD-LED subpixel.
 3. The display of claim 1, furthercomprising: a common electron injection layer over the common electrontransport layer in the OLED subpixel and the QD-LED subpixel; whereinthe common top electrode layer is over the common electron injectionlayer in the OLED subpixel and the QD-LED subpixel.
 4. The display ofclaim 1, further comprising: a common nanoparticle electron transportlayer comprising metal-oxide nanoparticles over the common quantum dotlayer in the OLED subpixel and the QD-LED subpixel.
 5. The display ofclaim 4, further comprising a common insulating layer between the commonquantum dot layer and the common nanoparticle electron transport layercomprising metal-oxide nanoparticles in the OLED subpixel and the QD-LEDsubpixel.
 6. The display of claim 1, further comprising: a buffertransport layer over the common quantum dot layer in the OLED subpixel;wherein the organic emission layer is over the buffer transport layer.7. The display of claim 1, further comprising: a buffer transport layerover the organic emission layer in the OLED subpixel.
 8. The display ofclaim 1, further comprising a common buffer transport layer over theorganic emission layer in the OLED subpixel, and over the common quantumdot layer in the QD-LED subpixel.
 9. The display of claim 1, furthercomprising: a common metal oxide nanoparticle hole transport layercomprising metal-oxide nanoparticles over the hole transport layer theOLED subpixel and the QD-LED subpixel; wherein the common quantum dotlayer is over the common metal oxide nanoparticle hole transport layerin the OLED subpixel and the QD-LED subpixel.
 10. A method of forming adisplay comprising: forming a common hole transport layer over a displaybackplane in using a first solution technique, wherein the common holetransport layer is formed over the display backplane in a hybrid pixelincluding an OLED subpixel and a QD-LED subpixel; forming a commonquantum dot layer over the common hole transport layer in the QD-LEDsubpixel and the OLED subpixel; evaporating an organic emission layerover the common hole transport layer in the OLED subpixel and over thecommon quantum dot layer in the OLED subpixel, wherein the organicemission layer comprises a phosphorescent material; evaporating a commonelectron transport layer over the common quantum dot layer in the QD-LEDsubpixel, and over the organic emission layer in the OLED subpixel; andforming a common top electrode layer over the common electron transportlayer in the OLED subpixel and the QD-LED subpixel.
 11. The method ofclaim 10, wherein forming the common quantum dot layer comprises using asecond solution-based technique.
 12. The method of claim 11, whereinevaporating the common electron transport layer comprises evaporatingthe common electron transport layer over the common quantum dot layer inthe OLED subpixel and the QD-LED subpixel.
 13. The method of claim 11,further comprising forming a common nanoparticle electron transportlayer comprising metal-oxide nanoparticles over the common quantum dotlayer in the OLED subpixel and the QD-LED subpixel using a thirdsolution-based technique.